Alloy



Patented Nov. 24, 1931 UNITED STATES PATENT OFFICE WILLIAM E. BUDER,

OF SCHENTECTADY, NEW YORK, ASSIG-NOR TO GENERAL ELECTRIC COMPANY, ACORPORATION OF NEW YORK.

ALLOY No Drawing. Application filed June 7,

My invention relates to alloys and has for its object the provision ofan alloy which is heat resisting or capable of withstanding .hightemperatures in 'air without excessive oxidation.

More specifically my invention relates to electric resistance heatingalloys and to alloys which may be cast to form various articles requiredto withstand high temperatures.

In carrying out my invention 1 provide an alloy having an iron, base andcontaining from 15 to 35f/ of chromium and from 5 to 12% of aluminum.Preferably I use 25% of chromium, and of aluminum,- the re- 15 mainderconsisting substantially of iron.

For the purpose of improving the physi cal quality of the alloy, about1% of a suit-1 able grain refining and purifying element may be added inmaking the alloy, such as titanium, zirconium, molybdenum, uranium,

all or a large portion of it may go off withvanadium or the like,although this is not absolutely necessary. The alloy mayand probablyWill' not contain the percentage of grain refining element added to themixture, since the slag.

This alloy may be forged or drawn into wire and has the othercharacteristics essential to a satisfactory resistance heating conductorsuch as durability or the property of withstanding hightemperatureswithout ex ces'sive oxidation, sufficient resistivity togenerate the required amount of heat when a current is passed throughit, and a zero temperw caturecoefficient of resistance throughout its"ohms per mil foot, and the durability also increases, while theductility becomes less. The temperature coeflicient of resistance is1923. Serial No. 644,058.

practically zero throughout the ranges of the various elements given,and the alloy shows very little oxidation when run for long periods attemperatures above 1000 0.] The composition ofthe alloy actually usedwould therefore 'be determined by the relativeimportance of cost of thematerials, resistivity, durability, and mechanical quality.

The metal forming the base of the alloy may be ordinary low carbon steelor even commercial iron. A steel containing .02% or less of carbon, .04%"or less of sulphur, or less of phosphorus and 0.15% or less of. siliconis satisfactory for my purpose.

In making the alloy it is preferable to use an electric furnace, sincethis furnace lends itself more readily to the cpntrolling of an alloy.The furnaceshould preferably have a basic lining since i an acid liningwere used a certain amount of silicon in the lining would be reducedby'the aluminum and enter into the alloy. Even a small-percentage ofsilicon in the alloy is objectionable. When the aluminum is not added inthe furnace but is added in the ladle, the basic lining becomes lessimportant.

The iron and chromium are melted in the furnace and then tapped on tothe aluminum, which has been preheated to a molten condition in theladle. Care should be taken to have the iron and chromium.mi-xturethor-' oughly deoxidized before adding' it to the aluminum. It ispreferable to have the carbon as low as possible in case thematerialused runs a little higher than approximately .01% in carbon, the carbonshould be reduced in the furnace before making the alloy. Thisappliesalso to the elements phosphorus and sulphur.. None of the furnaceslag should be allowed to come into contact with the alloy after thealuminum has been added. The molten aluminum and also the alloy after.the addition of. the aluminum should be kept covered with a special-slagof cryolite or a cryolite lime mixture to protect the-aluminum fromoxidation. Cryolite is used because of its solubility for aluminumoxide. Care should be takento have the metal in the furnace just hotenough to pour cleanly from the ladle but not superheated. The cooler itis when cast the better the grain obtained. When castingthe alloy eveprecaution should be taken to prevent oxi ation. This ay be done byfilling the molds beforehand ith a non-oxidizing 'gassuch as nitrogen',-:or carbon dioxide,- or bygdusting the molds lightly bug thoroughlyith cryolite to dissolve the oxide film forme between the ladle and themold. This revents the formation of cold-shutsand-su sequentc'racks'dueito' them. The cryolite method'is' preferredto the gasmethod.

While'I have described a specific embodiment of my inventioninaccordance with the provisions ofth patent statutes, it' should begunderstood thatI do'not'limit my invention thereto, since variousmodificaions thereof will suggest themselves. to those skilled in theart without departing from the -,spirit of my invention, the scope ofwhich is set forth in the annexed claims. What I claimasg-newvandidesire ,to secure by Letters Patent ojfthe UnitedStates'is 1. A heat resisting alloy containing ap- 1 proximately.of,chromium,,and 10% of aluminum, the'rem'ainder consisting of ironandnot more than 1%ofa gram refining element. 7

2. A heat resisting alloy having an iron, aozbase and containingapproximately 25% of chromium and 1 Q% 0f aluminum, there-2 mainderconsisting of an appreciable amount but not more-than 1%,of a grainrefining.

element.

= '35; 3. .A heat resisting alloy having an iron base and containingapproximately 25% of {chromium and 10% of aluminum, the remainderconsisting of-an appreciable amount but not' ;more than 1%;0fi-titanium;-v 1 4o 4.-A resistor containing about'25% chromium, about 10% aluminumand about 65% iron, said alloy having a substantially zerotemperature'coeificient of resistance throughout its normal operatingrange.

5 3 In witness ,Whereof, I have hereunto set my hand this 6th day ofJune, 1923. p

' WILLIAM'E; RUDER.

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